Method for producing cellulose/cellulose triacetate fabrics

ABSTRACT

Disclosed is a method for producing cellulose/cellulose triacetate fabrics. The method is characterized by the alkali treatment of a conjugated fabric comprising cellulose diacetate fibers with a degree of substitution of 2.0 to 2.75 and cellulose triacetate fibers with a degree of substitution of 2.75 or higher to convert the cellulose diacetate fibers into cellulose fibers.

TECHNICAL FIELD

[0001] The present invention relates to a novel method for producing fabrics in which cellulose is conjugated with cellulose triacetate.

BACKGROUND ART

[0002] Cellulose acetate fibers, such as cellulose diacetate fibers and cellulose triacetate fibers, are deacetylated or saponified with alkali to form cellulose fibers. Generally cellulose diacetate fibers can be more easily saponified, in comparison with cellulose triacetate fibers.

DISCLOSURE OF THE INVENTION

[0003] The present inventors, in consideration of the above fact, have conducted extensive studies into the production of cellulose/cellulose triacetate conjugated fabrics, resulting in the finding that strong alkai alone or in combination with weak alkali can selectively saponify the cellulose diacetate in cellulose diacetate/cellulose triacetate conjugated fibers, and various color tones can be expressed on the resulting conjugated fabrics consisting of cellulose and celluose triacetate, which have different intrinsic dyeing characteristics from each other.

[0004] Therefore, it is an object of the present invention to provide a novel method for producing cellulose/cellulose triacetate fabrics.

[0005] Based on the present invention, the above object could be accomplished by a provision of a method for producing a cellulose/cellulose triacetate fabric, wherein a conjugated fabric comprising cellulose diacetate fibers with a degree of substitution of 2.0 to 2.75 and cellulose triacetate fibers with a degree of substitution of 2.75 or higher is treated with alkali to convert the cellulose diacetate to cellulose.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0007]FIG. 1 is an IR spectrum of a cellulose fiber converted from of a cellulose diacetate fiber by the alkali treatment in Example 3.

[0008]FIG. 2 is an IR spectrum of the cellulose triacetate fibers of the fabric obtained by alkali treatment according to Example 3.

BEST MODES FOR CARRYING OUT THE INVENTION

[0009] Before the present method for producing cellulose/cellulose triacetate fabrics is disclosed or described, it is to be understood that the terminology used therein is for the purpose of describing particular embodiments only and is not intended to be limiting. The term “cellulose diacetate/cellulose triacetate fabrics” used as a raw material in the present invention means any fabric in which cellulose diacetate is conjugated with cellulose triacetate alone or in combination with other types of fibers.

[0010] Rayon fibers, which are artificial fibers with the same chemical structure as cellulose, are defined as regenerated cellulose fibers, in which 15% or fewer hydroxyl groups are substituted (Fibers Chemistry, Lewin Eli M. Pearce, Dekker p.914, 1985), and usually used in high-grade applications with favorable intrinsic brightness, specific gravity, and sense of touch.

[0011] Upon saponification of cellulose diacetate with alkali, its acetyl groups are converted to hydroxyl groups with concomitant rearrangement of molecular chains from an amorphous form to a crystalline form by folding or packing. Natural and regenerated cellulose fibers have the crystalline structures of cellulose I and II, respectively, while a mixed crystalline structure of cellulose II and IV is found in the cellulose fibers produced by saponification of cellulose diacetate, which are measured to have a crystallinity of 14 to 34% (by a gravimetric method) and a birefringence of 0.012 to 0.024.

[0012] Cellulose fibers obtained by the saponification of cellulose diacetate fibers are a kind of rayon fibers. The cellulose fibers prepared from cellulose diacetate range from 1.48 to 1.51 gm/cm³ in specific gravity, 1.2 to 2.5 gf/de in tensile strength, 20 to 50% in ductility, and 12 to 13% in moisture regain under standard conditions. These physical properties are similar to those of general rayon fibers.

[0013] In accordance with the present invention, the saponification of cellulose diacetate/cellulose triacetate fabrics is done with strong alkali, or with strong alkali and weak alkali in one bath or two baths.

[0014] Examples of alkali compounds useful in the saponification of the present invention include alkali metal hydroxides, such as sodium hydroxide, alkali earth metal hydroxides, such as calcium hydroxide, and alkali metal carbonates, such as sodium carbonate. Such alkali compounds may be used independently or in combination with a saponification promoter. Well known are those which are based on phosphonium or quaternary ammonium. Examples of commercially available saponification promoters include NEORATE NCB of Korea Fine Products, which is a phosphonium based saponification promoter; and KF NEORATE NA-40 of Korea Fine Products, DYK-1125 of IPPOSHA Co., Japan, DXY-10N of IPPOSHA Co., Japan, caserine PES of MEISEI CHEMICAL WORKS, LTD ., Japan, caserine PEL of MEISEI CHEMICAL WORKS, LTD., Japan, caserine PEF of MEISEI CHEMICAL WORKS, LTD., Japan, and SNOGEN PDS of Dae Young Chemical, Co., Korea, all being quaternary ammonium-based saponified promoter.

[0015] For use in saponification, alkali is used as an aqueous solution and in the amount of 10 to 60 wt % of cellulose diacetate fibers. The saponification to convert cellulose diacetate fibers to cellulose fibers is performed by dipping the conjugated fabrics in the aqueous alkaline solution at a temperature of 70° C. or higher, more preferably 70° C. to 130° C., for 1 to 120 minutes, once or twice.

[0016] When the cellulose/cellulose triacetate fabrics produced by the selective saponification of the present invention is treated with a disperse dye, which is usually used in dyeing of polyester, cellulose diacetate, cellulose triacetate, the cellulose fibers converted from cellulose diacetate remain undyed. On the other hand, a reactive dye can dye the converted cellulose fibers, but cannot dye the other fibers.

[0017] A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, but are not to be construed to limit the present invention.

[0018] In the following examples, a weight loss of a sample is defined as a percentage of a value obtained by dividing a difference between sample weights before and after alkali treatment with the sample weight before alkali treatment.

EXAMPLE 1

[0019] Polyester-conjugated satin fabrics (warp 70d/20f, warp density 283 ply/inch, weft 200d/57f, weft density 88 ply/inch) comprising, as warps, cellulose triacetate fibers with a degree of acetyl substitution of 2.9 or higher and, as wefts, diacetate fibers with a degree of acetyl substitution of 2.5, were scoured and dried. Into a liquid dyeing machine were charged the satin fabrics and water, along with NaOH at an amount of 38 wt % based on diacetate, followed by temperature elevation from 30° C. to 100° C. at a rate of 2° C./min. After the maximum temperature was maintained for 30min, the temperature was allowed to decrease to 30° C. at a rate of 2° C./min. Following the drainage of the liquid, the remaining alkali was removed by washing with water. Weight loss of the fabrics was measured to be 13.3%.

[0020] In the IR spectra of the resulting fabrics, obtained by use of IR spectroscopic analyzer (MAGNA 750, Nicolet, USA), a peak at 1760 cm⁻¹, corresponding to a cellulose carbonyl, disappeared from a portion which was initially cellulose diacetate, while the peak was found to remain in a portion which was initially cellulose triacetate. That is to say, there obtained fabrics in which cellulose, cellulose triacetate and polyester were conjugated.

[0021] The weight loss percentages of the alkali-treated fabrics were calculated and their cellulose fibers, along with untreated fabrics, were measured for physical properties. The results are given in Tables 2 and 3, below.

EXAMPLES 2 TO 5

[0022] The procedure of Example 1 was repeated except that the amount of NaOH was varied as described in Table 1, below. TABLE 1 Ex. NaOH Weight loss of No. (wt % based on diacetate) fabrics (%) 1 38 13.3 2 34 11.3 3 36 12.2 4 40 14.1 5 42 14.7

[0023] TABLE 2 Physical properties of cellulose fibers in fabrics Denier Breaking Breaking Specific Ex. No. (De′) strength (g/de) elong. (%) gravity 1 102.6 1.37 52.3 1.4986 2 120.3 1.21 43.8 1.4733 3 111.4 1.28 47.6 1.4815 4 102.3 1.36 51.9 1.4982 5 102.2 1.35 51.4 1.4981 Untreated 152.7 0.68 35.6 1.3120 diacetate

[0024] TABLE 3 Physical properties of cellulose triacetate in fabrics Denier Breaking strength Breaking Specific Ex. No. (De′) (g/de) elongation (%) gravity 1 77.2 1.11 29.7 1.302 2 77.6 1.12 30.2 1.301 3 77.6 1.12 29.9 1.302 4 75.9 1.08 25.5 1.310 5 75.1 0.94 19.0 1.323 Untreated 77.7 1.12 30.3 1.302

[0025] As stated above, cellulose diacetate fibers are reduced in denier, but increased in strength and elongation when the cellulose diacetate fibers are converted to cellulose fibers. In examples 1 to 3, it is confirmed that cellulose triacetate fibers are not changed in their physical properties. The fabrics obtained in Examples 4 and 5, whose weight loss was relatively high, were found to be reduced in the denier, strength and elongation of cellulose triacetate fibers, suggesting that saponification also occurred in the triacetate portion.

[0026] The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 

What is claimed is:
 1. A method for producing a cellulose/cellulose triacetate fabric, wherein a conjugated fabric comprising cellulose diacetate fibers with a degree of substitution of 2.0 to 2.75 and cellulose triacetate fibers with a degree of substitution of 2.75 or higher is treated with alkali to convert the cellulose diacetate to cellulose.
 2. The method as set forth in claim 1, wherein the conjugated fabric is treated with strong alkali, or a combination of strong alkali and weak alkali in one bath or two baths.
 3. The method as set forth in claim 2, wherein the alkali is added in combination with a saponifying promoter.
 4. The method as set forth in any one of claims 1 to 3, wherein the conjugated fabric further comprises a fiber different from cellulose diacetate and cellulose triacetate. 